Common screwdrivers and other currently available manual tools such as wrenches and torque devices suffer from a severe inefficiency due to a limitation of the human hand which operates the tool--namely the inability of the human hand to turn continuously in one direction. Since the hand which turns the screwdriver handle can only rotate a limited angle, the operation of any common manual tool whose handle is coaxial with the tool's main shaft consists of a repetition of the following cycle: first, the hand rotates the handle in the desirable direction for obtaining the function intended (tightening or loosening a fastener); second, the hand is rotated in the opposite direction to reposition it for the next cycle. During the second portion of the cycle, no advance is effected in the ultimate purpose of the tool (either because the hand slipped over the handle without entraining it, or because the tool is equipped with a one-way clutch such as a ratchet, or because the tool bit was extracted from engagement with the fastener and later reinserted). Therefore, this hand return stroke during the second portion of the cycle is completely wasted. The repetitive waste amounts to 50% of the hand motion and of the time consumed for each fastening job.
In an attempt to reduce this huge waste, certain tools (devices) have been invented which permit rotation of a tool bit in a same desirable direction, independent of which way a handle of the device is rotated. Most of these tools are of the torque wrench type in which two handles are mounted radially with regard to the tool axis. They are equipped with a rotation-reversal mechanism based on two ratchets. Since each ratchet tooth extends a certain angular span and any rotation of an angle smaller than that tooth span is lost motion, these tools do not make full use of the motion of the human hand and thus cannot completely eliminate the wasted motion. While offering only limited angular motion benefits, some of these tools are quite complex and require a large space clearance for their operation.
U.S. Pat. No. 1,860,914 (Wellman), issued on May 31, 1932, and U.S. Pat. No. 4,507,990 (Lack), issued on Apr. 2, 1985, illustrate the characteristics of some of these devices. Both patents describe ratchet wrenches with radial handles and they rely on the ability of ratchets to be deactivated (by disengaging a pawl from the teeth of its ratchet wheel) in order to switch from one direction of rotation of a main shaft to the opposite direction.
Other patents, such as U.S. Pat. No. 2,542,015 (Ellison), issued on Feb. 20, 1951, and U.S. Pat. No. 2,641,136 (Marsden), issued on Jun. 9, 1953, relate to devices which are quite impractical, because they turn the output shaft at different speeds (and, therefore, with different torques) depending on whether the input handle is rotated clockwise (CW) or counterclockwise (CCW).
U.S. Pat. No. 4,970,915 (Williams III), issued on Nov. 20, 1990, discloses a system usually comprising a motor and a handle as independent inputs which impart to an output shaft a unidirectional rotation (reversible through switching of a system of pawls/toothed rings or of a clutch with polygonal plate/rollers).
U.S. Pat. No. 5,176,038 (Inokuchi), issued on Jan. 5, 1993, discloses a motion-converting mechanism wherein a linearly reciprocating motion of a radial handle is converted through racks and pinions into a unidirectional rotation of an output shaft due to the work of toothed one-way clutches which can be selectively deactivated to reverse rotation of the output shaft. In one embodiment, the radial handle becomes a radial spring-returned rack pusher.
While these and other patents do achieve a certain reduction in the amount of wasted motion, they are generally quite complicated and therefore costly, and some of them have additional shortcomings.
It is desirable to provide a simple, sturdy, and practical mechanical rectifier useful as part of a manually operated tool which eliminates the wasted motion besetting common screwdrivers, or as part of a wave-powered electrical generator.